Gaseous fueled two-stroke engine

ABSTRACT

An engine according to various embodiments generates reduced emissions.

RELATED APPLICATIONS

The present application claims the benefit of priority of U.S. provisional patent application No. 61/306,569, entitled “GASEOUS FUELED TWO-STROKE ENGINE”, and filed Feb. 22, 2010, the entirety of which is incorporated by reference herein for all purposes.

BACKGROUND

Conventional two-stroke engines used in India and worldwide have certain disadvantages as they have high levels of pollutants in the exhaust pipe. This is primarily caused by lack of intake and exhaust valve as in the four-stroke engines, and secondly due to scavenging loss of fresh charge through the exhaust, and thirdly the fixed percent of oil is pre-mixed with fuel that does not readily burn during part throttle, and fourth due to liquid fuel as in gasoline engines does not vaporize readily. Most importantly, the exhaust gas has fractions of many different hydrocarbon species that is harder to treat by low cost catalysts.

It is known in the engine industry that there are gaseous fueled two-stroke engines with oil injection system. However, these engines do not have variable oil injection system and secondly do not have exhaust gas treatment to clean up the pollutants in the tail pipe.

The design described here according to some embodiments has a gaseous fueled two-stroke engine with oil injection system and a special catalyst to treat the hydrocarbon originating from the gas fuel, more particularly Propane fuel (commonly known as LPG) and Butane fuel as well as unburned hydrocarbon from the lubricating oil and a system to regulate percent of oil injected according to the operating ranges of the engine. The engine can be used in many hand-held applications such as trimmers, blowers, mopeds, and scooters.

SUMMARY

Accordingly, designs according to various embodiments provide new and improved methods of operating and having a cleaner gaseous fueled small two-stroke engine for many applications.

The low cost simpler two-stroke engine may be especially suited for hand-held, lawn and garden equipments such as trimmers, blowers, chainsaws, generator engines, and mopeds.

Various embodiments reduce the pollutants significantly while operating on gaseous fuel, more so with Propane (commonly known as LPG), Butane and natural gas.

Further, various embodiments provide a new and improved lubricating system where in the oil injection pump is driven off of the crankshaft for a positive oil feed into the engine and also regulated for optimum percent/amount of oil injected into the engine according to operating conditions of the engine. The oil pump can also be a diaphragm type operated due to pulsation in the crankcase chamber. Secondly, the oil is regulated by means of a link to the throttle valve, or intake manifold pressure or speed governor attached to the control system in the pump. The link can be from the throttle valve regulating the air-fuel in the carburetor or a pressure sensitive diaphragm in the intake.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a two-stroke engine having LPG fuel tank, pressure regulator and an oil pump.

FIG. 2 is a line diagram of the gaseous fueled engine system.

FIG. 3 is schematic of a string trimmer.

FIG. 4 is a schematic of a two-stroke engine having rotary valve intake system.

DETAILED DESCRIPTION

FIGS. 1, 2, and 3 illustrate exemplary embodiments of a two-stroke gaseous fueled oil injected engine with catalytic muffler for after treatment of the exhaust gas. The engine 100 includes an engine block 101, having a cylinder 102 with a reciprocating piston 110 with combustion chamber 108 on the upper side of the piston 110 and a crankcase chamber 105 on the bottom side. The engine block 101 has a crankcase 104 which could be a separate piece or an integral part of the cylinder as called a mono-block in some engines. The crankcase chamber 108 has crankshaft 106 which is supported by the bearings (not shown) in the crankcase 104. The crankshaft 106 has a crank web having a crank 118, with a crank pin 116. The piston 110 has a piston pin 114. The connecting rod 112 is movably connected to the crank pin 116 and the piston pin 114. The engine 100 has an intake port 136 and an exhaust port 134 in the cylinder 102. In some cases, the intake port may be on the crankcase 104 where the intake port is opened and closed by the rotary valve in the form of cut outs on the crank web (as in the case of Bajaj's scooter engine) as shown in FIG. 4, or a reed valve as in the case of TVS and Yamaha motor cycles. The crankcase chamber 105 is periodically in gaseous communication with the combustion chamber 108 through the transfer port 137 and transfer passage 107. The intake port 136 is connected through an intake manifold 126 to a gaseous carburetor assembly 122 having a gas carburetor, also known as gas delivery system 124 having a throttle valve 123 to regulate the flow of fuel and air. The exhaust port 134 has an exhaust muffler 128.

The exhaust muffler 128 is connected to the exhaust port and the exhaust muffler has an exhaust outlet 132 and a catalyst element 130 inside the exhaust muffler 128. There are many ways how the catalyst is mounted inside the exhaust muffler. Closer to the exhaust port is preferred; however, it may be mounted on a plate between the two shelves (not shown) of the exhaust muffler. In conventional petrol two stroke engines, the petrol is mixed with the lubricating oil in a certain ratio, ranging from 25:1 to 50:1. However, in a gaseous fueled two-stroke engine, the oil is inducted into the crankcase chamber through the intake manifold 126 or is directly injected into the crankcase chamber 108 using either gravity feed combined with the sub atmospheric pressure during intake or using a separate oil injection pump 138 driven by the crankshaft 106, as shown in FIGS. 1, 2, and 4. The oil tank 140 may be an integral part of the engine housing 304 or may be a separate part attached to the engine housing 304. The oil tank has a cap for refilling the oil or an oil tank may be a replaceable tank similar to the gaseous fuel tank. Where the oil tank is replaced each time the oil is below certain level. The important aspect of the oil tank is that the oil tank is of mostly a circular, semi-circular disc shape or ball shaped. Cylindrical or of any shape may be used. The shape may conform with the outline of the housing. Circular shape is preferred as the oil supply line 148 inside the tank is centrally mounted such that oil feed with filter (148) is free to rotate such that the oil inlet is always below the oil level in all (360 degrees) attitudes of the engine. This attribute is significant in a hand held portable engine, particularly in trimmer and chain saw applications. Therefore the oil feed 148 in the oil tank 140 is rotatably mounted in the tank and the pipe is of flexible material. The oil pump 138 may have control system 168 connected to the throttle valve 162 of the carburetor 124 through the linkage 166 to regulate the amount of oil injected into the engine and may vary directly with the position of the throttle shaft 164. The oil control system injects more oil at wide open throttle position and relatively less oil when the engine is operated at part throttle and idling. The oil pump may be an automatic pump varying the amount of oil per engine speed through a governor or may be designed to leak oil past its plunger at lower speeds. As such it is estimated that the oil consumption of the engine is no more than 6 percent of the fuel consumption and more than 1.5 percent of fuel consumption.

Another aspect of the engine with catalytic muffler is that a secondary air may be inducted through check valve into the manifold to improve converter efficiency. Yet, another aspect of the engine may be a temperature sensor on the engine block to shut off the engine in case engine runs hotter than pre-determined temperature due to lack of lubricating oil. The sensor is connected to the ignition coil for supply of power to operate the electronic sensor. Alternatively a pressure sensor in the oil delivery system may be incorporated or even an oil level sensor may be used as safety measure to protect the engine. Another aspect of the temperature sensor is that the control logic determines if the temperature difference between ambient temperature and engine block temperature is greater than the pre-determined range to shut off the engine. The power supply for the electronic control system may be from separate power coil 328 or built into the primary ignition coil 324 in the ignition coil. The ignition could be cut off based on the oil pressure sensor in the oil outlet line 146 (sensor not shown). It is also possible to have an oil level sensor to cut off ignition when the oil level is below the predetermined level. Also, it is possible to have a bimetal temperature sensor to cut off ignition when the temperature exceeds a predetermined engine temperature. The bimetal temperature sensor may be linked to the carburetor to cut off fuel when the temperature exceeds predetermined level.

FIG. 1 illustrates a piston ported gaseous fueled two-stroke engine, particularly used on many hand held agricultural equipment such as trimmers, blowers, chainsaws etc. In some embodiments, the engine may also be used in moped and scooters, generators, water pumps, etc. In some embodiments, the engine may also be used in industrial applications such as cutters, home improvement tools, etc. The engine 100 shown in FIG. 1 operates like a conventional two-stroke engine that one skilled in the art understands. As the piston 110 moves upward the intake port 136 is opened by the piston causing sub atmospheric pressure in the crankcase chamber 105. Thus the air fuel mixture is drawn into the crankcase chamber 105. Throttle valve 123 regulates the amount of air-fuel mixture entering the crankcase chamber. The oil is inducted or injected into the intake manifold 126, thus mixing the air-fuel with the mist of oil. The amount of oil injected is adjusted according to the throttle position and or engine speed. Amount of oil injected is more when the engine is operated at wide open throttle in comparison to low speed and or throttle position. The oil entering the crankcase chamber 105 thus lubricates the internal parts of the engine, such as bearings and piston, etc. As the piston moves upward, the charge in the combustion chamber is compressed and ignited by the spark plug 120. The burn gases expand as the piston moved downward developing power and driving the crankshaft 106 through the connecting rod 112. As the piston 110 moves downward, it opens the exhaust port 134 and the burnt gas is expelled into the combustion chamber. A few degrees later the transfer port 137 is opened by the piston, thus establishing a gaseous communication between the crankcase chamber 105 and the combustion chamber 108 through the transfer passage 107. The charge in the crankcase chamber 105 now under pressure flows into the combustion chamber 108 through the transfer passage 107. It is now apparent that during this phase, commonly known as scavenging process, both the transfer port and the exhaust ports are open for a few degrees of crank angles. As the piston moves upward it closes the transfer port 137 first and then the exhaust port 134. Further upward movement of the piston opens the intake port 136 starting the intake process and thus the cycle repeats every rotation of the crankshaft. The gaseous fuel carburetor 122 consists of a pressure regulator 404 and a metering chamber 406 and a fuel control valve 123. The fuel metering chamber 406 and pressure regular 404 are integral with the carburetor body 408. Pressure regulator 404 may be of multiple stages where the fuel pressure (approximately 200 to 100 psi) from the fuel tank 150 is reduced to about 35 psi in the high pressure regulator 154. It may be possible to have just one stage pressure regulator integral with the carburetor body 408. The gaseous fuel tank is preferably cylindrical in shape. The fuel tank is attached to the bottom of the crankcase 104 or in some case may be mounted on top above the cylinder block, as in the case of back pack blower or a brush cutter. The high pressure regulator 154 may be rigidly attached to the side of the engine block for transfer of heat from the engine block.

During the scavenging process, both the exhaust and transfer ports are open and this causes a fraction of the charge coming into the combustion chamber to escape through the exhaust port 134, which is the root cause for higher pollutants in the two-stroke engine. It is estimated that up to 30 percent of the charge escapes during the scavenging process and is commonly called short circuiting of charge. Some advanced engines use air-head concept (stratified engines) as published in U.S. Pat. No. 6,901,892 and U.S. Pat. No. 4,075,985 to minimize the short circuit loss of fuel. The exhaust gas mixed with unburned fuel (un-burnt hydrocarbons) escapes into the atmosphere after passing through the exhaust muffler 128 and the exhaust outlet 132. If the exhaust gas is not treated, the exhaust gas will have a variety of potentially toxic carbonaceous air pollutants. Pollutant is also known to cause cancers and respiratory diseases. Conventional two-stroke engines use catalysts in the exhaust muffler to clean the exhaust gas and reduce the levels of pollutants in the tail pipe exhaust gas. However, in a petrol engine, the oil is mixed at a fixed ratio, and importantly a variety hydrocarbon species is found in the exhaust gas. Thus composition of the catalyst has to be able to burn most of the species. Secondly, the particulate matters (PM) in petrol fueled two-stroke engine is significantly higher and the catalyst helps burn off some PM. However, in an LPG or Butane fueled two-stroke engine, since the fuel is already in gas form, the PM is almost zero and species of unburned hydrocarbon in the exhaust gas is very narrow and mostly propane or butane. As such treatment of the exhaust gas is easier with specific catalytic material. Particularly if the air-fuel mixture is lean, then it requires mostly reduction catalyst such as palladium. The use of catalytic muffler 128 in conjunction with the air-head engine will further reduce the exhaust pollutants.

FIG. 3 shows the construction of a gaseous fueled two-stroke engine with intake port controlled by the crank web 118. The crank web 118 has cut outs 117 and 118 that time the opening and closing of the intake port 126. Advantage of having the carburetor closer to crankshaft is that the throttle valve linkage 166 is connected to the oil control system 168 to regulate the amount of oil injected into the engine.

PARTS LIST

-   100 Gaseous fueled hand held engine with catalytic muffler -   200 Gaseous fueled rotary valve engine with catalytic muffler and     oil pump -   101 LPG Engine block -   102 Cylinder -   104 Crankcase -   105 Crankcase chamber -   106 Crankshaft -   107 Transfer passage -   108 Combustion chamber -   109 Transfer passage -   110 Piston -   112 Connecting rod -   114 Piston pin -   116 Crank pin -   117 Cut out A -   118 Crank (crank web) -   119 Cut out B -   120 Spark plug -   122 Carburetor assembly -   123 Throttle valve -   124 Gaseous fuel carburetor -   125 Air filter -   126 Intake manifold -   128 Exhaust muffler -   130 Catalyst element -   132 Exhaust outlet -   134 Exhaust port -   136 Intake port -   137 Transfer port -   138 Oil pump -   140 Oil tank -   142 Oil inlet to pump -   143 Oil supply line in the tank -   146 Oil outlet to the intake -   148 Oil feed with heavy filter -   150 Gaseous fuel tank -   152 High pressure fuel line -   154 Gas pressure regulator -   156 Low pressure fuel line -   162 Throttle valve -   164 Throttle shaft -   166 Linkage -   168 Oil control system -   200 Boom -   300 String trimmer -   304 Housing -   320 Engine temperature sensor -   324 Ignition coil -   326 Ambient temperature sensor -   328 power coil -   404 low pressure regulator -   406 Metering chamber -   408 Carburetor body

Various embodiments have been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. While there have been described herein, certain exemplary embodiments, other modifications shall be apparent to those skilled in the art from the teachings herein and, it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the described and contemplated embodiments. 

1. A gaseous fueled two-stroke engine 100 having a carburetor for gaseous fuel 124 with an oil injection pump 138 driven by a crankshaft 106 with an LPG or Butane fuel tank attached to the engine and a separate oil tank 140 and having a catalytic muffler 128 to reduce engine out unburned emissions from a gaseous fuel, and unburned emissions generated from oil, where the exhaust total emissions from muffler outlet are less than 50 gm/kw-hr.
 2. The engine as claimed in 1, having an intake port 136 and a temperature sensor to sense an ambient temperature at the intake port and to cut off ignition when the difference between the ambient temperature and an engine temperature is above a predetermined level.
 3. The engine as claimed in 1, having an oil pressure sensor to cut off ignition when an oil pressure in the oil outlet pressure is below a predetermined level.
 4. The engine as claimed in 1, having an oil level sensor in the oil tank 140 to cut off ignition when an oil level in the oil tank 140 is below a predetermined level.
 5. The engine as claimed in claim 1 having a catalytic muffler 128 for reducing exhaust emissions, in which the engine is a gaseous fueled small engine less than 100 cc.
 6. The engine according to claim 2 in which the muffler 128 includes a catalyst element 130 to reduce unburned propane fuel and unburned hydrocarbons generated from oil.
 7. The engine according to claim 2 in which the muffler 128 includes a catalyst element 130 to treat the unburned butane fuel.
 8. The engine according to claim 2 in which the muffler 128 includes a catalyst element 130 to treat unburned hydrocarbon.
 9. The engine according to claim 2 in which the muffler 128 includes a catalyst element 130 to reduce NOx, in which the engine is a lean burn gaseous fueled two-stroke engine.
 10. The engine according to claim 2 in which the muffler 128 includes a catalyst element 130 to oxidize unburned hydrocarbon in exhaust gas.
 11. The engine as claimed in claim 2 having Propane (LPG) as a fuel.
 12. The engine as claimed in claim 2 having Butane as a fuel.
 13. The engine as claimed in claim 1, in which the oil injection pump is a variable rate oil injection pump injecting substantially less oil per hour at idle speed than the oil injection rate at maximum speed.
 14. The engine as claimed in claim 1, in which the oil injection pump is a speed governed oil injection pump.
 15. The engine as claimed in claim 1, in which the oil injection pump is a throttle piston governed oil injection pump.
 16. The engine as claimed in claim 1, further including an electronic temperature sensor.
 17. The engine as claimed in claim 1, further including a bimetal temperature sensor to cut off the engine in the event that oil fails to be delivered to the engine, in order to protect against engine failure in such circumstances.
 18. The engine as claimed in claim 1 having an oil feed system having all attitude oil inlet 148 and shape of an all attitude oil tank
 140. 19. The engine as claimed in 1, in which the engine is a stratified two-stroke engine.
 20. The engine of claim 14 in which the oil feed system includes an oil feed line 148 that is rotatably mounted in the oil tank and has flexible oil line.
 21. A gaseous fueled two-stroke engine 100 having a gaseous carburetor 124 with an oil injection pump 138 driven by a crankshaft 106 with an LPG or Butane fuel tank attached to the engine and a separate oil tank 140 shaped such as to access oil at all engine attitudes and having a catalytic muffler 128 to treat the exhaust gas where the exhaust emissions are no more than 50 gm/kw-hr and the oil consumption is between 1.2 to 6% of fuel consumption rate.
 22. A gaseous fueled two-stroke engine 100 having a carburetor for gaseous fuel 124 with an variable rate oil injection pump 138 driven by a crankshaft 106 with an LPG or Butane fuel tank attached to the engine and a separate oil tank 140 and having a catalytic muffler 128 to reduce high engine out emissions to exhaust gas where the exhaust emissions are less than 50 gm/kw-hr and the gaseous fuel is substantially free of pre-mixed oil.
 23. A gaseous fueled two-stroke engine 100 having a carburetor for gaseous fuel 124 with an oil injection pump with a gaseous fueled tank attached to the engine and a separate oil tank 140 shaped such as to access oil at all engine attitudes and having a catalytic muffler 128 to treat the exhaust gas where the exhaust emissions are less than 50 gm/kw-hr and the gaseous fuel is substantially free of pre-mixed oil. 